Heavy oil recovery method

ABSTRACT

A hydrocarbon solvent such as benzene, platformate, or kerosene at a temperature in the range of 300* to 700* F. is injected into the top of tar sands at an injection well and forced through the formation to an adjacent production well. Injection of the solvent and production of oil are continued to maintain a gaseous phase across the top of the formation. The tar sand oil is made more mobile as a result of heating and dissolution of the solvent into the oil whereby the oil drains into the production well and is lifted to the surface.

United States Patent HEAVY OlL RECOVERY METHOD This invention relates tothe production of oil and more particularly relates to the production ofheavy, highly viscous oils from tar sands. l

Enormous quantities of hydrocarbons exist in known deposits ofhigh-density, high-viscosity oil in essentially unconsolidatedformations referred to as tar sands. Examples of such formations are theAthabasca and Peace River tar sands in Canada Oil in such formationsfrequently includes substantial amounts of asphaltic materials that areinsoluble in petroleum-naphthas. The oil may be highly viscous or evenof a semisolid bituminous nature, or may have a high pour point. Any oneof the properties alone may preclude recovery of oil from the tar sandsby primary production methods.

Although the permeability of some of the tar sands is sometimesrelatively high, because of the low mobility of the oil and the shallowdepth of many tar sands which preclude applying high pressures to thetar sands without breaking through the overburden, effective productionprocedures have not been developed. The unconsolidated nature of thedeposits prevents effective fracturing and propping of a fracture toform flow channels of high flow capacity and controlled location throughthe tar sand to production wells.

ln-situ combustion has been attempted as a method of producing the tarsands, but has not been successful because the permeability of the tarsands to flow is sharply reduced by the three phases of gas, water, andoil ahead of the combustion front. Furthermore, the oil ahead of thecombustion front remains cold and immobile. Attempts have been made toproduce heavy oils from tar sand by by creating a permeable channelthrough tar sands from an injection well to a production well, andthereafter injecting air into the channel. It was believed that oil fromthe formation would diffuse into the channel burn and thereby heat theoil in the tar sands the increase its mobility. Such procedures have notbeen successful because the air injected largely bypasses the oil in theformation, flows into the production well, and ignites oil in theproduction well. As a result of all of these difficulties, some havegone to an expensive mining and surface treating of the tar sands torecover the hydrocarbons.

This invention resides in a process for producing low gravity, highlyviseous oils from tar sands in which a hot hydrocarbon solvent such asbenzene, platformate, and kerosene is injected into the top of the tarsands at an injection well and forced through the formation to anadjacent production well. The temperature of the injected hydrocarbonsis high enough to maintain a gaseous phase to establish a permeablevaporfilled channel across the top ofthe formation. Oil flowing into theproduction well is lifted through the production at a rate maintaining apressure not substantially greater than atmospheric pressure in thcproduction well. As production continues, the upper portion of the tarsands is left filled with hydrocarbon vapors, or liquid of low viscosityformed by the condensation of hydrocarbon vapors, that can readily berecovered by a subsequent production step.

The single FIGURE of the drawings is a diagrammatic vertical sectionalview through injection and production wells extending downwardly througha tar sand.

Referring to the drawing, a tar sand l is shown penetrated by aninjection well indicated generally by reference numeral 12 and aproduction well spaced from the injection well and indicated generallyby reference numeral 14. Both wells l2 and 14 are shown extendingthrough an overburden 16 across the top of the tar sand 10, through thetar sand, and into an underlying formation 18.

The tar sand l0 is an incompetent or partially consolidated formationwhich can be parted bythe injection of fluid at a high rate but cannotbe fractured in the sense of creating a well-defined channel which canbe propped open. This invention can be used when the permeability of thetar sand is relatively high, preferably exceeding 100 millidarcies, topermit flow at significant rates through the formation at low pressuredifferentialsfrom the injection well to the production well.

The mobility of the oil in tar sand l0 is low enough to preventeconomically feasible production by primary production methods or bysimple fluid drive processes. This invention is particularlyadvantageous in the recovery from tar sands of oil that includessubstantial quantities of asphaltic materials that are insoluble inhighly paraffinie hydrocarbons such as propane, butane or even lightnaphthas or condensate. This invention is particularly valuable when tarsand l0 is relatively shallow and cannot be subjected to high pressures,and, therefore, the pressure available for driving oil through theformation is limited.

Injection well 12 has casing 20 extending downwardly into the underlyingformation 18. Casing 20 is cemented in place by conventional cementingprocedures, after which perforations 22 through the casing andsurrounding cement sheath are formed by any suitable method such as byuse of shaped charges in the interval of the tar sand near its upperboundary. lt is preferred that the perforations 22 be in the uppereighth of the tar sand 10. Casing 20 is capped at 24 and a tubing 26 runinto the casing through a packer 28.

Production well 14 is spaced from the injection well l2 at a desirabledistance, depending on the characteristics of the tar sand and the wellpattern, to give suitable production rates. lt is preferred that well 14be at a distance less than about 600 feet from well l2 to give 5 to l0acre spacing. Production well 14 has easing 30 extending downwardlythrough tar sand y10 into the underlying formation 18. Casing 30 iscemented in accordance with the conventional cementing procedures. Afterperforations 32 are formed in casing 30 and the surrounding cementsheath in the interval of tar sand 10 near its lower boundary, tubing 34is run into well 14 and held in plaec at its lower end by a packer 36set in casing 30 above the perforations. Tubing 34 extends through a cap38 closing the upper end of the well 14. A pump 40 is anchored in thelower end of the tubing 34 for lifting oil through the production well.

ln the method of this invention, a hot solvent is pumped down throughtubing 26 and injected through the perforations 22 into the upper partof tar sand l0.v The solvents should include hydrocarbons of low enoughboiling point to result in a vapor-filled zone extending across the tarsands in the area that has been swept free of reservoir oil. The gaseoussolvent will condense and dissolve in oil remaining in the vapor-filledzone and reduce its viscosity beyond the reduction resulting fromheating alone. Any liquid of low viscosity that is capable of beingvaporized at temperatures that will not cause cracking of the solvent orthe tar sand oil and is miscible in the tar sand oil withoutprecipitating constitutes in the oil can be used as the solvent.Preferred solvents because of their rela tively low cost and goodsolvent properties are aromatic hydrocarbons or mixtures of hydrocarbonscontaining substantial amounts of aromatic hydrocarbons. Examples ofsuch hydrocarbons are benzene, toluene, xylene, and highly aromaticmixtures of hydrocarbons having a boiling point range substantially thesame as gasoline. Kerosene can also be used. Highly paraffinichydrocarbons such as LPG, light naphthas or condensate are not suitablebecause of their inability to dissolve asphaltic constituents of the tarsand oil. Condensate composed principally of paraffinic hydrocarbons hasbeen found to cause precipitation of asphalt from Athabasca or PeaceRiver tar sands even though the condensate was approximately 70 percentCland contained only about 7 percent C3 and C4.

The solvent is injected preferably in the vapor phase at a temperaturein the range of 300 to 700 F. lt is preferred that the temperature ofthe injected solvent be as high as possible without causing substantialcracking of the solvent as it passes down tubing 26 and into the tarsand l0. ln any event, the temperature of the solvent should exceed itsinitial boiling point at the formation pressure in the tar sand. Onentering the tar sand l0, solvent will remain in the vapor phase in theupper part of the tar sands where the reservoir has been flushed out.Where the solvent vapor contacts reservoir oil, the solvent willcondense and dissolve in the oil in the tar sands. The raising of thetemperature of the oil in the tar sands and the dilution of the oil bythe hot solvent greatly increase the mobility of the oil in the tar sandl0. Continued injection of the hot solvent results in extension of avapor-filled zone 42 across the top of the tar sand from well l2 to well14. The single phase in the zone greatly increases the permeability ofthe formation to the injected solvent and allows circulation from theinjection well to the production well at a low pressure differential.

During the injection of hot solvent at the injection well, oil is pumpedfrom the production well by pump 40. lnjection and production arecontinued after the solvent breaks through at the production well toheat the tar sands adjacent the production well and reduce theproduction well and reduce the pressure in the tar sands adjacent theproduction well to less than the vapor pressure of the solvent at theprevailing temperature. The maximum pressure which can be maintained inthe reservoir adjacent the production well will, therefore, depend onthe particular solvent used and the temperature of the solvent. lfbenzene is the solvent used and the temperature adjacent the productionwell is 400 F., for example the pressure at the production well may beas high as 200 p.s.i. Higher pressures can be maintained if thetemperature is increased. A low pressure, for example less than l p,s.i.and even as low as atmospheric pressure can be attained, adjacent theproduction well and is advantageous in increasing the volumes of the hotvapors and thereby increasing their effectiveness in driving oil fromthe formation.

Injection of hot solvent at well l2 and production of oil at well 14 iscontinued at a rate to extend a vapor phase zone 42 all of the wayacross thc tar sand from the injection well to the production well. Thevapors cone downwardly at the production well toward the perforations 32and thereby cause the lower boundary of the vapor zone to slopedownwardly. Oil adjacent well 14 drains by gravity drainage into thewell through perforations 32. Oil in the tar sand directly below zone 42is heated and diluted by the hot solvent. The resultant mixture has ahigh mobility and flows along the lower boundary of zone 42,particularly along the downwardly sloping boundary of the productionwell 14, and drains into production well 14 through perforations 32. lfpart of the oil in the tar sand is vaporized it flows into zone 42 andis swept by the hot vaporized solvents to well 14. The downwardlyflowing vapors mix with the heated oil near the production well andfurther reduce the viscosity of the oil flowing into the well.

The oil entering well 14 is lifted by pump 40 to the surface. Continuedinjection of hot solvent through well l2 and production of oil throughwell 14 cause zone 42 to bc gradually enlarged downwardly. When thelower boundary of zone 42 approaches the lower boundary of the tar sandl0, or the viscosity of the remaining tar sand oil has been reduce byheating or dilution with solvent, the hot solvent injection is stopped.The solvent and low viscosity oil remaining in the tar sand can bereadily displaced through the tar sand to the production well by atertiary recovery process such as water or insert gas flooding. Forwardcombustion can also bc used to displace the remaining oil.

lt is essential to this invention that the hot solvent be injected intothe formation near its upper boundary. lf hot solvent is injected into alower part of the tar sand, oil above the level of injection made fluidby the hot solvent drains downwardly into the vapor zone, condenses thehot solvent, and prevents the rapid establishment of a well-to-wellvapor zone.

This invention has been described for a production well havingperforations 32 near the lower boundary of the tars and l0 from thebeginning of the operation. Perforations could initially be made nearthe upper boundary of the tar zone and then, as the zone 42 is enlarged,new perforations made at successively lower positions, in each instancebelow the lower boundary of the zone 42, and the packer 36 successivelyresets just above the lowest perforations. Oil made mobile or fluid byheat and dilution will still flow into the production well by gravitydrainage, but will not have as far to drain.

lclaim: l. A method of producing heavy asphaltic oil from a tar sandcomprising injecting into the upper portion of the tar sand at aninjection well penetrating the tars and a hot fluid consistingessentially of a hydrocarbon solvent selected from the group consistingof at least one aromatic hydrocarbon selected from the group consistingof benzene, toluene and xylene, mixtures containing a high concentrationof such aromatic hydrocarbons with nonaromatic hydrocarbons of ofsubstantially the same boiling point, and kerosene; the temperature ofthe hot solvent injected into the formation being in the range of 300 to700 F. such that the temperature exceeds the initial boiling point ofthe solvent at the tar sand formation pressure to form a vapor zoneextending substantially horizontally across the tar sad near the lowerboundary thereof at a production well production well spaced from theinjection well; and continuing the injection of the hot solvent toextend the vapor zone in the tar sand to the vicinity of the productionwell and heat oil in the tar sand below the vapor zone whereby saidheated oil whereby said heated oil drains to the production well.

LColumn Eggg UNITED STATES PATENT QFFICE CERTIFICATE OF CORRECTIONPatent No. 3, 608, 638 Dated September 28, 1971 Inventor(s) Paul L.'lerwilliger It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column l, line 9, insert after "Canada" Column l, line l3, "the" shouldread "those" Column l, line 23, "sand" should read "sands" Column l,line 30, "sand" should read "sands" Column l, line 30, delete "by"second occurrence Column l, line 34, insert after "channel" Column l,line 34, cancel "the", third occurrence Column 2, line 49, "constitutes"should read "constituents" Column 3, line 13 delete "and reduce theproduction well" Column 3, line 25, "volumes" should read "volume"Column 3, line 39, "of" should read "near" Column line 3 "reduce" shouldread "reduced" Column line 8, "insert" should read "inert" Column line18, "tars and" should read "tar sand" line 23, "resets" should read"reset" Column line 30, "tars and" should read "tar sand" Column 4,

Column 4, line 35, delete "of" second occurrence line 4l, "tar sad"should read "top of the tar sand J formation, withdrawing oil from thetar sandI lines 45 and 46, delete "whereby said heated oil" secondoccurrence Column 4,

Signed and sealed this Zth day of June 'I 972.

(SEAL) Attest:

ROBERT GOT'I'SCHALK EDWARD MTLETGHERJR.

Commissioner of Patents .Attesting Officer

1. A method of producing heavy asphaltic oil from a tar sand comprisinginjecting into the upper portion of the tar sand at an injection wellpenetrating the tars and a hot fluid consisting essentially of ahydrocarbon solvent selected from the group consisting of at least onearomatic hydrocarbon selected from the group consisting of benzene,toluene and xylene, mixtures containing a high concentration of sucharomatic hydrocarbons with nonaromatic hydrocarbons of of substantiallythe same boiling point, and kerosene; the temperature of the hot solventinjected into the formation being in the range of 300* to 700* F. suchthat the temperature exceeds the initial boiling point of the solvent atthe tar sand formation pressure to form a vapor zone extendingsubstantially horizontally across the tar sad near the lower boundarythereof at a production well production well spaced from the injectionwell; and continuing the injection of the hot solvent to extend thevapor zone in the tar sand to the vicinity of the production well andheat oil in the tar sand below the vapor zone whereby said heated oilwhereby said heated oil drains to the production well.